PROJECT SUMMARY Older adult women are at unique risk for negative outcomes of insufficient physical activity (PA). Mobile health interventions using wearable activity monitors have shown promise for increasing walking for PA, but adherence to PA recommendations declines sharply over time. To improve adherence in this at-risk population, we propose to test an innovative method of framing mobile health devices and apps. As opposed to the more typical corrective frame, a celebratory frame focuses on positive aspects of the target behavior. This approach is rooted in Self-Determination Theory, which posits that autonomous regulations (motivations related to enjoyment, identity, and values) are more powerful predictors of behavior than controlled regulations. We propose to use a socially networked active game to emphasize aspects of walking PA that are enjoyable and related to older womens' identity and values, thus increasing their autonomous regulation for PA and in turn PA adherence. The CHALLENGE study (Challenges for Healthy Aging: Leveraging Limits for Engaging Networked Game-based Exercise) will consist of an initial sub-study followed by a large randomized controlled intervention trial. During the sub-study, we will conduct cognitive interviews among 20 older women to ensure that refinements to the game after our pilot trials are acceptable. Then, we will randomize 300 women (aged 65 ? 85, <150 minutes/day PA, with access to a mobile device with Internet access and a camera) into the game intervention or to an active control. Participants in the game intervention will receive an activity monitor and access to a private Facebook social network group. In the group, interventionists will post challenges weekly that are specifically framed to follow principles of celebratory technology and game development best practices. Participants will post photos and text related to the challenges (e.g., photos of their favorite place in their neighborhood and an explanation of what it means to them). The intervention will continue for one year. Participants randomized to the control will receive only the activity monitor. Assessments will occur at baseline, intervention midpoint (6 months), intervention end (12 months), and after a 6-month maintenance period (18 months). The primary outcome will be steps, measured objectively using research-grade accelerometers. We will also investigate motivational variables and engagement in the social network, to better characterize the mechanisms through which the intervention impacts PA. This project has the potential to move forward research, theory, and practice due to its systematic development, integration of game principles and theoretical constructs, and potential to improve health of a population at unique risk at a public health level.